This invention relates to an actuator which comprises a lever and a longitudinal-effect electroexpansive transducer for actuating the lever. A longitudinal-effect electroexpansive transducer comprises a transducer block in which an electrostrictive longitudinal effect in a broader sense is resorted to. A lever actuator according to this invention is specifically useful as an impact printer unit to be employed in combination with a plurality of similar impact printer units as an impact printer head of a dot-matrix printer. This invention relates, more particularly, to the mechanical structure of the lever actuactor although a longitudinal-effect electroexpansive transducer is therein used.
The transducer block is of an axially elongated shape. Responsive to an actuating voltage supplied to the transducer block axially thereof, a strain is reversibly generated therein to axially extend or contract the transducer block. Inasmuch as contraction is a sort of extension unless compressive and tensile strengths are in question, the word "electroexpansive" should be understood to include the notion of "electrocompressive."
The transducer block has a pair of end surfaces. One is supported by a base member of the actuator. Responsive to the strain, the other end surface moves relative to the base member. The lever is supported by a fulcrum at a point, the fulcrum point. The strain generated in the transducer block is transmitted to the lever as a power or force onto another point, the power point. In an impact printer unit, a printing element is carried as a weight or load by the lever at still another point, the weight point, even when a specific weight, such as the printing element, is not carried by the lever.
An actuator comprising a longitudinal-effect electroexpansive transducer is revealed in U.S. Pat. No. 3,614,486 issued to Parker C. Smiley and assigned to Physics International Company and later in U.S. Pat. No. 3,649,857 issued to La Verne F. Knappe, assignor to International Business Machines Corporation. As will later be discussed with reference to one of more than thirty figures of the accompanying drawing, a longitudinal-effect electroexpansive transducer is more preferable in such an actuator than a transducer in which an inverse piezoelectric transverse effect or the like is resorted to.
It has now been found and confirmed as will later be described with reference to a few of the accompanying drawing figures that actuation of the lever in a conventional actuator of the type described results in development of a stress, typically in the transducer block, to such an extent that the stress would degrade the actuator. In this connection, it is worthwhile to note that the transducer is strong against a compressive stress but is weak against tensile and bending stresses. Furthermore, the actuation deforms the base member. The degradation therefore takes place in the transducer block, at an interface of attachment between the transducer block and the base member, and/or in the base member. In addition, development of the bending stress means that electrical energy is wasted in bending the transducer block and others. The degradation therefore occurs also in the efficiency of conversion of electrical energy to mechanical or kinetic energy.